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This article mainly shows you the "Example Analysis of Si9000 RF Line Impedance Calculation". The content is simple and easy to understand, and the organization is clear. I hope it can help you solve your doubts. Let Xiaobian lead you to study and learn the article "Example Analysis of Si9000 RF Line Impedance Calculation".

SI9000 Description

First of all, we should choose the matching impedance design model, which is illustrated by the coplanar impedance model of oil cover, as shown in the figure below.

H1----The thickness of the medium between the outer layer and the next outer layer. Jiali Chuang plate indicates the finished thickness of 7628PP, the factory thickness of 7628PP with low glue content is 7.6mil, and there is glue loss when pressing, so the unified value is 7.1, which is about equal to the value.

W2---Line width on impedance line. The width of the top of the trace indicates the meaning of side corrosion. The copper thickness of the outer layer finished product 1oz is generally calculated according to the side corrosion amount of 1 mil.

W1---Line width under impedance line. Finished line width, that is, our drawing design line width. Track width is generally rounded design, such as 4.0mil, 4.5mil, 5.0mil, 5.5mil, 6.0mil.

D1---Distance between impedance line and coplanar reference VCC/GND. It indicates the spacing of ground copper next to the routing distance, regardless of the design spacing of corrosion. The two sides next to the routing indicate the large copper skin of ground copper.

T1---Impedance line copper thickness or finished copper thickness = substrate copper thickness + plating copper thickness.

Er1---Dielectric constant of dielectric layer. Here is the dielectric constant of PP.

CEr1---Solder resistance dielectric constant.

C1---Solder resist thickness of substrate. Solder resist thickness on the substrate between traces, note that the trace gap is generally small, easy to produce gully effect, the solder resist thickness here is slightly thicker.

C2---Resistance welding thickness of wire surface (post-processing).

Zo---impedance value required.

using skills

1) The corresponding value can be calculated if there is a "calculate" button. For example, after other parameters are input, the required value can be calculated. In the case of fixed laminated structure, there are not many calculation buttons used. Only impedance and line width are calculated from each other. Other values are basically determined. The line width can be calculated according to the specified impedance value. On the contrary, the impedance value can be calculated according to the impedance width. Track width is generally rounded design, such as 4.0mil, 4.5mil, 5.0mil, 5.5mil, 6.0mil..., Generally, input the required impedance value first, reverse the width of the trace, and then adjust the width value according to the nearest principle, as shown in the figure below, the impedance value is 50.6ohm, and the impedance is usually controlled at 50±5ohm, but this is no problem. The width of the trace is not rounded, but 1 decimal place can be reserved in mil units.

2) The two columns of "minimum value" and "maximum value" in the figure are colored. If the color direction is consistent, it means proportional, and if the direction is opposite, it means inversely proportional. The direction of W and Zo in the following figure is opposite, indicating that both are inversely proportional, that is, the wider the trace, the smaller the impedance, and the thinner the trace, the larger the impedance value. This is useful for calculating the differential impedance line width adjustment line spacing later.

3) Reference layer: The first layer of ground copper (some are grids) encountered at the same position of the impedance line is called the reference layer, and these ground copper are also called signal shielding layers relative to the impedance line.

coplanar impedance calculation

Here, coplanar impedance is designed using JLC7628 laminated structure. The laminated structure of JLC76278 four-layer board is as follows:

The parameters of JLC7628 laminated structure were obtained.

parameters

numerical

description

H1

7.1mil

PP thickness is 7.1 mil when calculating outer impedance.

PP thickness is 8.1 mil when calculating inner impedance.

Er1

4.6

Dielectric constant PP4.6

W1

design line width

W2

Related to actual processing, Jiali Chuang W2=W1-1mil

D1

design spacing

T1

0.035mm(1.378mil)

1oz copper thick

C1

0.8mil

Substrate Solder Resistance 0.8mil

C2

0.5mil

Solder resistance of routing surface 0.5mil

CEr

3.8

The following are some of the design-related pad or device pad width parameters:

Most chip pin width is 0.25mm, 0402 capacitor pad width =19.685mil=0.5mm, 0201 capacitor pad width =11.811mil=0.35mm;

During design, try to avoid line width and device pad size to keep consistent;

The following figure shows a 50ohm impedance line designed using JLC7628 laminate structure, W1=10mil, D1= 7.5 mil, design impedance 50.38 ohm;

Note: The impedance processed by the actual factory will be different from the design, and it can be maintained at 50±5 ohms. In actual production, you can ask the factory for the impedance test strip of the corresponding plate.

The above is "Si9000 RF line impedance calculation example analysis" all the content of this article, thank you for reading! I believe that everyone has a certain understanding, hope to share the content to help everyone, if you still want to learn more knowledge, welcome to pay attention to the industry information channel!

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